Composite showerhead electrode assembly for a plasma processing apparatus

ABSTRACT

A method of forming an elastomeric sheet adhesive bond between mating surfaces of an electrode and a backing member to accommodate stresses generated during temperature cycling due to mismatch in coefficients of thermal expansion. The elastomeric sheet comprises a thermally conductive silicone adhesive able to withstand a high shear strain of ≧300% in a temperature range of room temperature to 300° C. such as heat curable high molecular weight dimethyl silicone with fillers. Installation can be manually, manually with installation tooling, or with automated machinery.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims benefit of the filing date of U.S. ProvisionalApplication Ser. No. 61/008,152 filed Dec. 19, 2007, the entire contentof which is incorporated herein by reference.

BACKGROUND

Plasma processing apparatuses are used to process substrates bytechniques including etching, physical vapor deposition (PVD), chemicalvapor deposition (CVD), ion implantation, and resist removal. One typeof plasma processing apparatus used in plasma processing includes areaction chamber containing upper and bottom electrodes. An electricfield is established between the electrodes to excite a process gas intothe plasma state to process substrates in the reaction chamber.

SUMMARY

In an embodiment, a composite showerhead electrode assembly forgenerating plasma in a plasma processing apparatus is provided. Thecomposite showerhead electrode assembly includes a backing platecomprising top and bottom surfaces with first gas passages therebetween,the bottom surface having bonded and unbonded regions, the first gaspassages having outlets in unbonded regions to supply a process gas toan interior of the plasma processing apparatus, an electrode platehaving a top surface, a plasma exposed bottom surface, and second gaspassages extending therebetween and in fluid communication with thefirst gas passages, wherein the second gas passages have inlets inunbonded regions of the top surface of the electrode plate, and anelastomeric sheet adhesive joint disposed between mating surfaces ateach of the bonded regions which allows movement in a lateral directionof the electrode plate relative to the backing plate during temperaturecycling due to mismatch of coefficients of thermal expansion in theelectrode plate and the backing plate.

In another embodiment, a method of joining components for a compositeshowerhead electrode assembly for a plasma processing apparatus isprovided. A first surface of a sheet of uncured elastomeric adhesive isapplied to a bottom surface of a backing member in a predeterminedpattern of regions to be bonded which exclude regions to remainunbonded, the backing member having a top surface and a plurality offirst gas passages extending between the top surface and the bottomsurface and having outlets in unbonded regions. A top surface of anelectrode is applied to a second surface of the uncured elastomericsheet adhesive in a predetermined pattern of regions to be bonded, theelectrode having a plasma exposed bottom surface and a plurality ofsecond gas passages extending between the top surface and bottom surfaceof the electrode, wherein the second gas passages have inlets inunbonded regions of the top surface of the electrode. The top surface ofthe electrode is bonded to the bottom surface of the backing member bythe elastomeric sheet adhesive therebetween, wherein the second gaspassages are in fluid communication with the first gas passages.

Another embodiment provides a method of processing a semiconductorsubstrate in a plasma processing apparatus. A substrate is placed on asubstrate support in a reaction chamber of a plasma processingapparatus. A process gas is introduced into the reaction chamber withthe composite showerhead electrode assembly. A plasma is generated fromthe process gas in the reaction chamber between the showerhead electrodeassembly and the substrate. The substrate is processed with the plasma.

In still another embodiment, a composite showerhead electrode assemblyfor a plasma processing apparatus is provided which includes a backingmember having a bottom surface with regions to be bonded, excludingregions to remain unbonded, and a plurality of first gas passagesextending between the bottom surface and a top surface of the backingmember, wherein the first gas passages have outlets in regions to remainunbonded, to supply a process gas to an interior of a plasma processingapparatus; an electrode to generate plasma in the plasma processingapparatus, the electrode having a top surface with regions to be bondedand a plurality of second gas passages in fluid communication with thefirst gas passages, the second gas passages have inlets in regions toremain unbonded, extending through the electrode from the top surface toa plasma-exposed bottom surface of the electrode; and an uncuredelastomeric sheet adhesive to be cured in a joint between matingsurfaces of each of the regions to be bonded to allow movement in thelateral direction of the electrode relative to the backing member duringtemperature cycling due to mismatch of coefficients of thermal expansionof the backing member and electrode, wherein the sheet of elastomericadhesive is a filled, heat-curable, unvulcanized elastomeric siliconesheet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-sectional view of a portion of an embodimentof a composite showerhead electrode assembly and a substrate support fora plasma processing apparatus.

FIG. 2 is a partial top view of an embodiment of an inner electrode,illustrating the application of an adhesive in a predetermined patternin relation to gas passages.

FIG. 3A illustrates a cross section portion of an embodiment of thebacking plate shown in FIG. 1 supporting a bead of uncured paste orliquid adhesive prior to bonding; FIG. 3B illustrates the cross sectionshown in FIG. 3A after the inner electrode is bonded to the backingplate with the paste or liquid adhesive.

FIGS. 4A and 4B illustrate a cross section portion of an embodiment ofthe inner electrode shown in FIG. 1 bonded to the backing plate withsheet adhesive.

FIGS. 5A-5C illustrate an embodiment of a sheet adhesive cuttingpattern.

FIG. 6 shows a cross section of an embodiment of sheet adhesive in theform of flat rings and a flat ring having an elevation jog to be placedon the backing plate shown in FIG. 1.

FIG. 7 illustrates a detail of an embodiment of a flat ring of sheetadhesive having an elevation jog shown in FIG. 6.

FIG. 8 illustrates a detail of a recess in the backing plate shown inFIG. 6.

FIG. 9 illustrates a cross section of an embodiment of a backing plate.

FIG. 10 illustrates embodiments of a sheet adhesive having differentcoplanar properties.

FIG. 11 illustrates an embodiment of a sheet adhesive having elevationjogs.

FIG. 12 illustrates embodiments of sheet adhesive in various shapes.

FIG. 13 illustrates an embodiment of a sheet adhesive.

FIG. 14 shows a shear test result conducted at room temperature forsheet adhesive Example 1.

FIG. 15 shows a shear test result conducted at 180° C. for sheetadhesive Example 2.

FIG. 16 shows a fatigue test result conducted at 180° C. for sheetadhesive Example 3.

FIG. 17 shows a shear test result conducted at 180° C. for sheetadhesive Example 3 after the fatigue test.

DETAILED DESCRIPTION

Control of particulate contamination on the surfaces of semiconductorwafers during the fabrication of integrated circuits is essential inachieving reliable devices and obtaining a high yield. Processingequipment, such as plasma processing apparatuses, can be a source ofparticulate contamination. For example, the presence of particles on thewafer surface can locally disrupt pattern transfer duringphotolithography and etching steps. As a result, these particles canintroduce defects into critical features, including gate structures,intermetal dielectric layers or metallic interconnect lines, resultingin the malfunction or failure of the integrated circuit component.

Reactor parts with relatively short lifetimes are commonly referred toas “consumables,” for example, silicon electrodes. If the consumablepart's lifetime is short, then the cost of ownership is high. Siliconelectrode assemblies used in dielectric etch tools deteriorate after alarge number of RF hours (time in hours during which radio frequencypower is used to generate the plasma). Erosion of consumables and otherparts generates particulate contamination in plasma processing chambers.

Showerhead electrode assemblies can be fabricated by bonding two or moredissimilar members with mechanically compliant and/or thermallyconductive bonding materials, allowing for a multiplicity of function.The surfaces of components can be treated with a primer to enhanceadhesion of the bonding material. To enhance electrical or thermalconductivity, the bonding material can contain electrically and/orthermally conductive filler particles. However, the primer and thefiller particles associated with use of the bonding material can also bea potential source for particulate contamination. Additionally, becauseshowerhead electrode assemblies contain gas passages, it is essentialthat the flow of the bonding material be controlled, such that the gaspassages remain unobstructed by the bonding material. Methods forjoining components of a plasma processing apparatus are provided thatcan reduce contamination originating from the bonding material andprecisely control bonding material placement.

FIG. 1 illustrates an exemplary embodiment of a showerhead electrodeassembly 10 for a plasma processing apparatus in which semiconductorsubstrates, e.g., silicon wafers, are processed. The showerheadelectrode assembly is described, for example, in commonly-owned U.S.Patent Application Publication No. 2005/0133160, which is incorporatedherein by reference in its entirety. The showerhead electrode assembly10 comprises a showerhead electrode including a top electrode 12, abacking member 14 secured to the top electrode 12, and a thermal controlplate 16. A substrate support 18 (only a portion of which is shown inFIG. 1), including a bottom electrode and optional electrostaticclamping electrode, is positioned beneath the top electrode 12 in thevacuum processing chamber of the plasma processing apparatus. Asubstrate 20 subjected to plasma processing is mechanically orelectrostatically clamped on an upper support surface 22 of thesubstrate support 18.

In the illustrated embodiment, the top electrode 12 of the showerheadelectrode includes an inner showerhead electrode member 24, and anoptional outer ring electrode 30 (i.e. an outer electrode member 301.The inner electrode member 24 is preferably a cylindrical plate (e.g., aplate composed of silicon) and includes plasma-exposed bottom surface 26and top surface 28. The inner electrode member 24 can have a diametersmaller than, equal to, or larger than a wafer to be processed (e.g., upto about 8 inches (about 200 mm) or up to about 12 inches (about 300 mm)if the plate is made of silicon). In a preferred embodiment, theshowerhead electrode assembly 10 is large enough for processing largesubstrates, such as semiconductor wafers having a diameter of 300 mm orlarger. For 300 mm wafers, the top electrode 12 is at least 300 mm indiameter. However, the showerhead electrode assembly can be sized toprocess other wafer sizes or substrates having a non-circularconfiguration. In the illustrated embodiment, the inner electrode member24 is wider than the substrate 20.

For processing 300 mm wafers, the outer electrode member 30 is providedto expand the diameter of the top electrode 12 from about 15 inches toabout 17 inches. The outer electrode member 30 can be a continuousmember (e.g., a continuous poly-silicon ring), or a segmented member(e.g., including 2-6 separate segments arranged in a ring configuration,such as segments composed of silicon). In embodiments of the topelectrode 12 that include a multiple-segment, outer electrode member 30,the segments preferably have edges, which overlap each other to protectan underlying bonding material from exposure to plasma and do not havegas passages therein. The inner electrode member 24 preferably includesa pattern or array of gas passages 32 extending through the backingmember 14 for injecting process gas into a space in a plasma reactionchamber located between the top electrode 12 and the bottom electrode18. Optionally, the outer electrode member 30 also includes a pattern orarray of gas passages (not shown) extending through a backing ring 36 ofthe backing member 14 for injecting process gas into the space in theplasma reaction chamber located between the top electrode 12 and thebottom electrode 18.

Silicon is a preferred material for plasma exposed surfaces of the innerelectrode member 24 and the outer electrode member 30. Both electrodesare preferably made of high-purity, single crystal silicon, whichminimizes contamination of substrates during plasma processing and alsowears smoothly during plasma processing, thereby minimizing particles.Alternative materials that can be used for plasma-exposed surfaces ofthe top electrode 12 include SiC or AlN, for example.

In the illustrated embodiment, the backing member 14 includes an innerbacking plate 34 and an outer backing ring 36, extending around theperiphery of the backing plate 34. The backing plate 34 includes abottom surface 38. In the embodiment, the inner electrode member 24 isco-extensive with the backing plate 34, and the outer electrode member30 is co-extensive with the surrounding backing ring 36. However, thebacking plate 34 can extend beyond the inner electrode member 24 suchthat a single backing plate can be used to support the inner electrodemember 24 and the segmented outer electrode member 30. The innerelectrode member 24 and the outer electrode member 30 are attached tothe backing member 14 by a bonding material. A radio frequency (RF) ringgasket 80 can be located between the inner electrode member 24 andbacking plate 34 near the outer periphery of the inner electrode member24. The backing member 14 contains a plurality of holes 40 adapted toreceive fastener members 42 for attaching the backing member 14 tothermal control plate 16. Backing plate 34 also includes multiple gaspassages 44 extending through the backing plate 34 and in fluidcommunication with the gas passages 32 in inner electrode member 24.Optionally, backing ring 36 also includes multiple gas passages (notshown) extending through the backing ring 36 and in fluid communicationwith optional gas passages (not shown) in the outer electrode member 30.

The backing plate 34 and backing ring 36 are preferably made of amaterial that is chemically compatible with process gases used forprocessing semiconductor substrates in the plasma processing chamber,and is electrically and thermally conductive. Exemplary suitablematerials that can be used to make the backing member 14 includealuminum, aluminum alloys, graphite and SiC. A preferred material forbacking plate 34 and backing ring 36 is aluminum alloy 6061 which hasnot been anodized.

The top electrode 12 can be attached to the backing plate 34 and backingring 36 with a suitable thermally and electrically conductiveelastomeric bonding material that accommodates thermal stresses, andtransfers heat and electrical energy between the top electrode 12 andthe backing plate 34 and backing ring 36. The use of elastomers forbonding together surfaces of an electrode assembly is described, forexample, in commonly-owned U.S. Pat. No. 6,073,577, which isincorporated herein by reference in its entirety.

In an embodiment, the elastomeric joint is an elastomeric sheetadhesive. The sheet adhesive can be any suitable elastomeric materialsuch as a polymer material compatible with a vacuum environment andresistant to thermal degradation at high temperatures such as above 200°C. The elastomeric material can optionally include a filler ofelectrically and/or thermally conductive particles or other shapedfiller such as wire mesh, woven or non-woven conductive fabric.Polymeric bonding materials which can be used in plasma environmentsabove 160° C. include polyimide, polyketone, polyetherketone, polyethersulfone, polyethylene terephthalate, fluoroethylene propylenecopolymers, cellulose, triacetates, silicone, and rubber.

Preferably, the sheet adhesive is a thermally conductive siliconeadhesive bonding an upper electrode aluminum (Al) backing plate to asingle crystal silicon (Si) showerhead. Preferably, the adhesivewithstands a high shear strain of at least 200% (for example, 200 to500% or 200 to 300%) in a temperature range from room temperature to180° C. or higher (for example, from room temperature to 300° C.). Alsopreferably, the adhesive withstands a high shear strain of at least 300%(for example, 300 to 500%) in a temperature range of room temperature to180° C. or higher (for example, room temperature to 300° C.). Theadhesive can require on the order of 340 psi shear stress to achieve300% strain (at room temperature to 180° C. or higher). Preferably, theadhesive requires on the order of 20 to 300 psi shear stress to achieve300% strain (at room temperature to 180° C. or higher). For example, theadhesive can require 20-50 psi, 50-100 psi, 100-200 psi, or 200-300 psishear stress to achieve 300% strain (at room temperature to 180° C. orhigher). Most preferably, the adhesive can require on the order of 20-80psi shear stress to achieve 200-400% strain (at room temperature to 180°C. or higher). It is preferred that the adhesive exhibits a linear shearstress/strain curve up to at least 200% or up to at least 300% in thetemperature range from room temperature to 180° C. or from roomtemperature to 300° C., however nearly linear is also preferred. Alsopreferably, the adhesive has the lowest possible maximum shear stress atits ultimate failure, for example, less than or equal to 80 psi shearstress at 400% strain (in the temperature range from room temperature to180° C. or room temperature to 300° C.).

Preferably, when the electrode plate is a disk of single crystal siliconwith a diameter of at least 200 mm, the sheet adhesive exhibits a linearshear stress/strain curve up to at least 200% or up to at least 300% inthe temperature range of room temperature to 180° C. or room temperatureto 300° C., from a shear stress of 20 to 340 psi after about 5,000temperature cycles of heating the electrode assembly from roomtemperature to 250° C.

When the aluminum backing plate and silicon showerhead thermally expandat different rates, the adhesive used to bond the two parts togethercouples the loads between the two parts. In contrast, when the adhesiveis soft (low shear stress at a given strain according to an embodiment),the two parts will not induce stresses or diaphragm deflections intoeach other. Preferably, the backing plate and showerhead have a gapbetween non-bonded areas of the two mating surfaces. Diaphragmdeflections can cause non-bonded areas of the backing plate surface tocontact and rub along non-bonded areas of the showerhead surface duringthermal expansion of the two parts. Such rubbing can wear particles offof one or both surfaces. Also when diaphragm deflections are present inthe upper electrode assembly, higher localized contact loads can occurwhere the aluminum backing plate mates with the thermal control plate.This can lead to galling between the backing plate and the thermalcontrol plate, generating particles within the system. Thus, when theadhesive is soft, less particulate contamination is generated due tolittle or no diaphragm deflection and little or no galling between thebacking plate and thermal control plate from part distortion due tomismatching thermal coefficients of expansion.

The sheet adhesive can be formulated purely with high molecular weightdimethyl silicone and optional fillers, or it can also be matrixedaround fiberglass screen (scrim), metallic screen, or mixed with glassmicrobeads and/or nanobeads of glass or other material to accommodaterequirements of various applications. Preferably, the sheet adhesive isformulated with high molecular weight dimethyl silicone matrixed aroundAl₂O₃ microbeads. Composite layers of sheet adhesive can be produced andlaminated which have different physical properties. In a preferredembodiment, coplanar areas of the sheet adhesive can be discretelyformulated with different physical properties. Examples of physicalproperties are thermal conductivity, elasticity, tensile and shearstrength, thickness, thermal coefficient of expansion, chemicalresistance, particle erosion, and service temperature range.

For example, filled elastomer material may be subject to plasma erosionand has the potential of releasing conductive filler particles duringplasma processing. During plasma processing, ions or radicals maymigrate into gas passages 32 causing the erosion of the filled elastomermaterial at the joint interface around the holes. For example, aluminumalloy filler particles which originate from plasma eroded elastomermaterial can deposit on the wafer to produce defects during the etchingprocess. In an embodiment for reducing the release of conductive fillerparticles, coplanar areas of the sheet adhesive can be discretelyformulated with different filler particle densities. For example, areasof the sheet adhesive in the joint interface exposed to ions or radicalsthat have migrated through gas passages 32 can be unfilled (fillerparticle free) while coplanar areas of the sheet adhesive not exposed tothe ions or radicals can include filler particles.

Preferably, the high purity elastomeric material of the elastomericsheet adhesive is a heat curable thermally conductive silicone based ona diphenyl dimethyl silicone copolymer. The preferred elastomeric sheetadhesive is formulated from a thermally conductive room temperatureunvulcanized silicone sheet under the trade name HCR-9800-30 availablefrom NUSIL TECHNOLOGY. Preferably, the silicone sheet adhesive productuses an Al₂O₃ filler and is formulated to be heat curable, that is,preferably, the sheet adhesive does not require a separate activatorapplication to initiate a cross-linking reaction. Preferably, the sheetadhesive is formulated with a suitable heat activated component toperform the cross-linking reaction at a predetermined curingtemperature, for example, the heat activated crosslinking agent can be aperoxide. Such formulated adhesive sheet is available from NUSILTECHNOLOGY.

In the case where the elastomer is an electrically conductive elastomer,the electrically conductive filler material can comprise particles of anelectrically conductive material. Potential electrically conductivematerials for use in the impurity sensitive environment of a plasmareaction chamber are nickel coated carbon powder, nickel powder, carbonnano-tubes, graphene, graphite and a combination thereof.

In the case where the elastomer is a thermally conductive elastomer, thethermally conductive filler material can comprise particles of athermally conductive metal or metal alloy. A preferred metal for use inthe impurity sensitive environment of a plasma reaction chamber is analuminum alloy, aluminum oxide (Al₂O₃) or boron nitride (BN). Preferablythe elastomeric sheet adhesive has a low strength, can withstand a highshear strain and has a high thermal conductivity. Preferably, thethermal conductivity is at least 0.5 W/mK, more preferably at least 0.8W/mK and most preferably at least 1.0 W/mK. A more uniform distributionof thermal and/or electrical conductor particles can be achieved in anelastomeric sheet adhesive than in a liquid or paste elastomeric bondingmaterial.

In order to stay within the elastic limits of the finally formed joint,a suitable bond thickness can be used. That is, too thin of a sheetadhesive joint could tear during thermal cycling whereas too thick asheet adhesive joint could reduce the thermal conductivity between theparts to be joined. It is not necessary to use an electrically and/orthermally conductive elastomer since sufficient RF power can be suppliedto the electrode through a thin area of the elastomeric joint due tocapacitive coupling between the electrode and the support member.

FIG. 1 shows an embodiment where a plurality of recesses 48 are locatedin the backing plate 34 having flat rings of sheet adhesive 52 locatedtherein to bond the mating surfaces of the inner electrode member 28 andthe backing plate 38. The embodiment in FIG. 1 shows a recess 54 havinga greater depth to accept a flat ring sheet adhesive 56. This embodimentalso shows an RF gasket 80 between the inner electrode member 24 and thebacking plate 34 near the periphery of the inner electrode member 24. Inthe embodiment of FIG. 1, the outer ring electrode 30 can be bonded tothe backing ring 36 by a single flat ring of sheet adhesive 60 in arecess in the backing ring 58.

The mating surfaces of the electrode and support member can be planar ornon-planar. For instance, one mating surface can be planar and the othercan include a recess for receiving the sheet adhesive bonding material.Such a recess, for example, can protect the sheet adhesive from exposureto plasma. Alternatively, the mating surfaces can be contoured toprovide an interlocking and/or self-aligning arrangement. In order toenhance adhesion of the elastomeric bonding material, the matingsurfaces are preferably coated with a suitable primer. When the bondingmaterial is formulated from the NUSIL TECHNOLOGY HCR-9800-30 materialdescribed above, the primer can be silicone primers under the trade nameSP-120 or SP-270 manufactured by NUSIL TECHNOLOGY. Preferably, suchprimer is applied to the mating surfaces and dried prior to placing thesheet adhesive on the surface locations to be bonded.

The primer can be applied as a thin coating by any suitable techniquesuch as wiping, brushing, spraying, preferably on discrete bondingsurfaces of the showerhead assembly components to create bonding sitesfor the later applied bonding material. If the primer contains asolvent, application of the primer by wiping can enhance bonding bycleaning the surfaces. A siloxane containing primer reacts with air andcreates silicon bonding sites when cured in air at room temperature.Such primers provide a visual indication of the amount of bonding siteswith excessive primer locations appearing powdery.

The sheet adhesive is preferably between transfer sheets for handling.Preferably the transfer sheets are TEFLON manufactured by DUPONT.Transfer sheets are preferred to prevent, for example, deformation anddamage to the uncured sheet adhesive. The sheet adhesive is applied tothe mating surfaces or primed mating surfaces by removing one transfersheet and applying the exposed surface of the adhesive sheet to a firstmating surface, removing the other transfer sheet and applying a secondmating surface to the other exposed surface of the adhesive sheet. Theadhesive sheet surface can be tacky and preferably, tooling can be usedto precisely remove the transfer sheets and place the sheet adhesive onthe mating surfaces. Also preferably, the adhesive sheet on the matingsurface can be placed under a vacuum to draw out any gaps or voids underthe adhesive and apply a temporary seating load, such as by vacuumbagging.

After the sheet adhesive bonding material is applied to at least one ofthe surfaces, the parts can be assembled such that the surfaces arepressed together under compression, under a static weight, or byatmospheric pressure within a vacuum bag. Since the elastomer is in theform of a sheet adhesive it is not necessary to apply an initial slightpressure such as hand pressure to spread the elastomer throughout thejoint to be formed. However a slight pressure such as hand pressure orlight atmospheric load within a vacuum bag is required to seat theadhesive to the mating surfaces. After approximately five minutes orless of seating load, it is preferred to remove all loading on theadhesive. The curing should preferably be performed without anysignificant static weight or vacuum bag loads. The bond can be cured atelevated temperature in an atmospheric or protective gas environment.The assembly can be placed in a convection oven and heated to activatethe crosslinking process of curing the bond. For example, a heat curablebond material can be treated at a primary cure temperature of between110° C. and 122° C. (e.g., 116° C.) for 10 to 20 minutes (e.g., 15minutes). Upon successful inspection of the assembly, the bond materialis treated at a secondary cure temperature of between 140° C. and 160°C. (e.g., 150° C.) for 1.5 to 2.5 hours (e.g., 2 hours). Alternatively,only the secondary cure can be applied for 2.5 to 3.5 hours (e.g., 3hours), skipping the primary cure.

Preferably, the sheet adhesive maintains its geometric shape such thatthe sheet adhesive does not bulge or flow during bonding and curing.However, the sheet adhesive volume change during curing can be up to 5%volume shrinkage. Preferably, the sheet adhesive undergoes no more than2 to 3% volume shrinkage during curing.

During plasma processing, the elastomer bonded electrode assemblies areable to sustain high operation temperatures, high power densities, andlong RF hours. Also, the use of sheet adhesive elastomer materials as amechanism for joining electrode assemblies has additional advantagesover non-sheet adhesives during plasma processing of semiconductorwafers.

Regions of the components with residual unused primer (unbonded areas)can be a source of contamination. For example, the use of siloxaneprimers (e.g., RHODIA SILICONES VI-SIL V-06C) has been determined tohave potential to introduce levels of contamination, including titanium.The titanium contaminants may potentially react with the siliconsubstrate, forming titanium silicides in undesired regions of thesubstrate during the etching process.

A sheet adhesive allows reducing contamination originating from theprimer material by selectively applying the primer to regions on theshowerhead assembly (e.g. joining inner electrode member 24 with backingplate 34) where sheet adhesive bonding material will be subsequentlyapplied, rather than coating all surfaces with the primer. FIG. 2 is atop view of inner electrode member 24, including a plurality of gaspassages 32 extending through to a bottom plasma-exposed surface 26. Inthis embodiment, the sheet adhesive elastomeric material is applied asannular zone patterns 46 between regions containing gas passages 32.However, prior to applying the elastomeric material, primer can beapplied in the same annular zones pattern corresponding to theelastomeric material.

While the sheet adhesive is shown as applied in annular zones, thepattern of applying sheet adhesive is not limited and can be applied inother patterns such as zones which are not annular. Sheet adhesive canbe cut in any desired pattern and portions removed from the transfersheet to allow transfer of discrete sections of the sheet adhesive tothe parts to be joined.

The primer can be applied to the top surface 28 of the inner electrodemember 24 in a predetermined pattern of bonding regions, surrounded byunbonded regions. In one example, the primer 46 can be applied byrotating inner electrode member 24 about its center point C, andapplying the primer in patterns 46 with a dispenser (e.g., a felt-tipdispenser) by contacting one or more outlets of the dispenser at asingle position or multiple radial positions relative to the centerpoint C, generating one or more annular zones at a time. In anotherexample, the annular zones pattern (or any desired pattern) can beapplied by covering the top surface 28 of the inner electrode member 24with a mask having openings in a predetermined pattern. However, theprimer may be applied in any appropriate predetermined pattern (e.g., aplurality of discrete zones, radial and/or discontinuous annular zones),as long as the primer is applied only to regions underlying the sheetadhesive elastomer material. The primer can also be applied by wiping,brushing, spraying through the openings of the mask. Both of the abovedescribed methods can also be used for applying primer to the bottomsurface 38 of backing plate 34. In applying the primer to only selectedregions 46 underlying the sheet adhesive elastomeric material,contaminants associated with the application of the primer can besignificantly reduced.

Examples of mask materials can include KAPTON®, a polyimide-basedmaterial, MYLAR®, a polyester-based material, or TEFLON®, afluoropolymer resin, all available from DU PONT.

Another advantage the sheet adhesive has over liquid, gel and pasteadhesives is control of flow or elimination of flow. For example, asshown in FIG. 3A, when the showerhead assembly components to be joinedcontain gas passages 32/44, the flow of liquid or paste uncuredelastomeric material 50 must be controlled when the components arepressed together before the elastomer is cured. When the uncured paste50 is applied between two components and pressed, it is difficult tocontrol the flow of the uncured elastomer material. As shown in FIG. 3B,the uncontrolled flow of the uncured elastomeric material 50 can resultin the obstruction or blockage of the gas passages 32/44. As a result,additional cleaning or machining can be required to clear the obstructedor blocked gas passages 32/44. The sheet adhesive elastomeric materialcan avoid such problems since the sheet adhesive 52 can be placedbetween the showerhead assembly components to be joined with much finertolerances than a liquid or paste elastomeric material as shown in FIG.4A. The sheet adhesive can be configured to exhibit good volume controlso as to not ooze or flow into undesired areas. As such, the sheetadhesive elastomeric material 52 can be located closer than the liquid,paste or gel, to the gas passages 32/44 without risk of obstruction orblockage of the gas passages 32/44.

When the top electrode 12 and the backing member 14 are composed ofmaterials with different coefficients of thermal expansion, thethickness of the elastomer material can be varied to accommodate thedifferences in thermal expansion. For example, the top electrode 12 canbe silicon and the backing member 14 can be metallic (e.g., aluminum,stainless steel, copper, molybdenum, or alloys thereof). However, if twocomponents with greater differences in thermal expansion coefficientsare bonded (i.e., aluminum and silicon), upon heating during temperaturecuring or during operation of the electrode, a non-uniform shear stressis generated in the elastomeric bonding material, due to the differentrates of thermal expansion. For example, if a circular aluminum backingmember 14 is concentrically bonded to a circular silicon top electrode12, the shear stress in the elastomeric bonding material near the centerof backing member 14 and top electrode 12 is minimal at an elevatedprocessing temperature. However, the outer portion of the aluminumbacking member 14 undergoes a larger amount of thermal expansion thanthe outer portion of the silicon top electrode 12. As a result, when thetwo materials are bonded, the maximum shear stress occurs in the outerperipheral edge of the backing member 14 or top electrode 12, where thedifference in thermal expansion is greatest.

Adhesive in a sheet form can provide exceptional bond thickness controlto precisely control parallelism of bonded surfaces over large areassuch that inserts or spacers are not required to control bond thicknessor parallelism. FIG. 4A shows an embodiment of the sheet adhesive 52bonded to a recess 48 in the bottom surface of the backing plate 34between gas passages 44. FIG. 4B shows the sheet adhesive 52 bonded tothe bottom surface 38 of the backing plate 34 and the top surface 28 ofthe top electrode 24 between gas passages 32/44.

The sheet form allows exceptional volume control to limit or preventoozing of adhesive into unwanted areas. The application of the sheetadhesive obviates need for precision dispensing equipment used to applya liquid or paste adhesive. Issues with feed speeds of automated and/ormanual dispensing procedures, and associated drying, necking or globingof adhesive dispense beads are thus eliminated. The sheet adhesive hasmore uniform suspension of thermal conductivity filler, an anticipatedbetter shelf life, and can provide a more efficient and reliablemanufacturing process.

Pre-form sheet adhesive shapes can be designed to conform to irregularlyshaped planar features, and can be optimized to maximize surface contactarea with the mating parts. For example, in FIG. 3A, the bead of liquidor paste adhesive 50 contacts the backing plate 34 along a curvedsurface of the bead 50 shown in cross section in recess 48. The contactarea between the bead 50 and the mating surface of the backing plate 38is narrower than the bead 50 and difficult to control uniformity andreproducibility of the bond. In FIG. 3B, when the electrode 24 is matedto the backing plate 34 the contact between the liquid or paste adhesivebead 50 and the mating surfaces of the backing plate and the electrode38/28 is limited and difficult to control such that the contact area maybe less than the diameter of the bead 50, requiring an excess of liquidor paste adhesive to achieve a desired contact area for suitable bondstrength and thermal and/or electrical conductivity between the backingplate 34 and the electrode 24.

In FIG. 4A, the elastomeric sheet adhesive 52 precisely contacts thebacking plate 34 along a predetermined surface of the adhesive sheetshown in cross section in recess 48 parallel to the backing platesurface. The contact area between the adhesive sheet 52 and the matingsurfaces 38/28 of the backing plate 34 and the electrode 24 provides amaximum ratio of contact area to volume of elastomeric adhesive as shownin FIG. 4B. The greater contact area of the sheet adhesive 52 allows forless elastomeric sheet adhesive 52 to be used in a bond to achievesuitable thermal and/or electrical conductivity, bond strength and bondelasticity between the backing plate 34 and the electrode 24.

Preferably, the sheet adhesive can be cut into pre-form shapes, by, forexample, laser, water jet, die cut, plotter cutting and other cuttingmethods. The sheet adhesive can also be cast into pre-form shapes by,for example, casting such as tape casting, rolling or ink jet printing.FIGS. 5A-C show a preferred embodiment where sheet adhesive 100 is cutinto flat rings 52. FIG. 5A shows a plan view of the sheet adhesive 100and flat rings 52 of various inner and outer diameters, i.e., the flatrings can have various planar widths. FIG. 5B shows an edge view of thesheet adhesive embodiment in FIG. 5A. FIG. 5C shows a detailed view ofarea “A” of the sheet adhesive embodiment in FIG. 5A illustrating sheetadhesive rings of narrow planar width and large diameter cut from sheet100. For example, sheet adhesive 100 can be 0.012 inches (305 μm) thickand flat rings 52 can have inner and outer diameters in inches of(0.195, 0.464), (0.854, 1.183), (1.573, 1.902), (2.725, 3.625), (4.449,4.778), (5.168, 5.497), (6.320, 7.220), (8.043, 8.372), (9.196, 10.096),(10.919, 11.248), (11.638, 11.724), and (11.913, 12.000).

Preferably, the sheet adhesive and flat rings of sheet adhesive 52 arecut, handled and transferred as laminates between transfer sheets ofTEFLON (not shown). FIG. 6 shows a cross section of the flat rings ofsheet adhesive 52 positioned over recesses 48 in the mating surface 38of the backing plate 34 (the backing plate 34 is inverted). Suchrecesses 48 are in the form of racetrack grooves. Although notpreferred, a flat ring of sheet adhesive can have an elevation jog. FIG.6 shows a flat ring sheet adhesive 56 has an elevation jog such that theflat ring has a varying thickness along its planar width. The flat ringsheet adhesive 56 matches a racetrack groove 54 in the backing plate 34.FIG. 7 shows a detailed view “B” of the elevation jog in the sheetadhesive ring 56 shown in FIG. 6 wherein the sheet adhesive ring isthicker in the center of the ring. Such an elevation jog can be made,for example, by laminating flat rings of sheet adhesive having differentradial widths and/or different axial heights (thickness). FIG. 8 shows adetailed view “D” of the recess 54 in the backing plate 34 formed toaccept the sheet adhesive ring 56.

FIG. 9 shows a detailed view “E” of the backing plate 34 (non-inverted)shown in FIG. 6. The recesses 48 in mating surface 38 can be located toprecisely control the bonded and unbonded regions. The unbonded regionscan be 1 to 95% of the surface area of the mating surface 38. Forexample, the unbonded region can be 1-5%, 5-10%, 10-15%, 15-20%, 20-30%,30-40%, 40-50%, 50-60%, 60-70%, 70-80%, 80-90%, or 90-95% of the surfacearea of the mating surface 38. The gas passages 44 are in the unbondedregions and the sheet adhesive bonds the bonded regions. A distancebetween an edge of a sheet adhesive, for example, a flat ring 52 inneror outer diameter and a gas passage 44 opening in surface 38 can beprecisely controlled to optimize bond properties and as previouslymentioned, eliminate risk of blockage of gas passages 44 by oozing orbulging of a non-sheet elastomeric adhesive. Preferably, the sheetadhesive essentially maintains its original size and maintains the sameshape before, during and after curing with little or no shrinkage, forexample, 2-3% volumetric shrinkage after curing.

As a preferred embodiment the sheet adhesive can be composite layers offlat rings of various planar width having one or more different physicalproperties in a thickness direction (laminated) or a planar direction(co-planar). FIG. 10 shows a portion of a flat ring sheet adhesive 102having different co-planar physical properties. For example, innerportion 62 and outer portion 64 can be unfilled silicone elastomer sheetadhesive for low particulate contamination release and middle portion 66can contain Al₂O₃ particles for thermal conductivity.

FIG. 11 shows an embodiment of a sheet adhesive 104. The sheet adhesive104 may be a plurality of flat circular or semi-circular rings ofvarious widths having elevation jogs 68 (small steps). Surfaces 70 and72 may bond to recesses in an electrode mating surface (not shown, butsimilar to recesses 48, 54 and 58 in backing member 14) or surface 70may bond to an electrode mating surface without recesses such as theinner electrode mating surface 28 and/or the mating surface of outerelectrode ring 30. Surfaces 74 and 76 may bond to recesses in a backingmember 14 mating surface similar to recesses 48, 54 and 58 or surface 76may bond to a backing plate and/or backing ring mating surface withoutrecesses (not shown).

By way of example, the sheet adhesive can be arranged as an uniform ornon-uniform pattern of dots, triangles, columns and other geometricshapes of various widths and thicknesses without limitation. FIG. 12shows cones 106, rectilinear strips 108, triangles 110, circular dots112 and circular dots having elevation jogs 114 of sheet adhesive. Thesheet adhesive can be a plurality of such geometric shapes to bond thebonding regions on the mating surfaces of the backing member 14 andelectrode 12. However, in another embodiment the sheet adhesive can be asingle sheet having a “spider web” geometric shape to precisely match tobonding regions while leaving unbonded regions for gas passages 32/44.FIG. 13 shows an embodiment of a single sheet 116 in plan view forbonding, for example, mating surfaces 28 and 38. Accordingly, spaces 78in the sheet adhesive 116 can correspond to unbonded regions. In thisembodiment such unbonded regions would correspond to greater than 90% ofthe mating surface area.

Before curing, the sheet adhesive preferably has a physically stablenature. The sheet adhesive before curing is an unvulcanized,uncross-linked composition having dimensional stability. The uncuredsheet adhesive can be malleable. As mentioned, transfer sheets arepreferred for handling the uncured sheet adhesive to prevent deformingthe sheet adhesive before curing. Upon heating, a cross-linking agentsuch as a peroxide filler preferably cures the sheet adhesive in theoverall same shape as the uncured sheet adhesive. After curing, thesheet adhesive returns to the same shape after mechanical forces areremoved. Greater contact area control increases thermal and/orelectrical conductivity between the adhered parts. The cured sheetadhesive also maintains comparable elasticity at high volumes of fillerparticles to that of the cured gel elastomers and greater elasticity athigh volumes of filler particles than the cured liquid and pasteelastomers. By using high volumes of filler particles in the elastomericsheet adhesive greater thermal and/or electrical conductivity can beachieved between the adhered parts for a given volume of elastomericadhesive without sacrificing bond strength or elasticity.

Preferably, pre-form shapes are installed into captivating cavities 48of the mating assembly. Installation can be performed by such methods asmanually, manually with installation tooling, or with automatedmachinery. The adhesive sheet can be formulated to have limited orunlimited work time, and then heat cured when curing is convenient.

As illustrated in FIGS. 4A and 4B, backing member 34 is joined to innerelectrode 24 such that the first gas passages 32 of the inner electrode24 and the second gas passages 44 of the backing member 34 are in fluidcommunication. To enhance adhesion, a primer 46 can also be applied tobottom surface 38 of the backing member 34 in the same predeterminedpattern as applied to the top surface 28 of inner electrode member 24.In alternative embodiments, backing member 34 or inner electrode member24 may contain plenums to distribute one or more gas supplies in adesired gas distribution pattern. In another embodiment, gas passages 32can be in fluid communication with one or more gas passages 44.

In a preferred embodiment, the sheet adhesive bonds the top surface ofthe electrode 28 to the bottom surface of the backing plate 38 such thatthere is a 51 to 381 μm (0.002 to 0.015 in) gap therebetween in unbondedregions. For example, a depth of the recess 48 on the backing platebottom surface and/or the electrode top surface is preferably 102 to 508μm (0.004 to 0.020 in), for example 100 to 200 μm or 200 to 500 μm. Morepreferably, the recess 48 is 178 μm (0.007 in) deep. However, thebacking plate bottom surface and the electrode top surface can be bondedby the sheet adhesive without a recess. Also preferably, the sheetadhesive bonds the backing plate bottom surface parallel to theelectrode top surface with a distance between the two mating surfacesvarying by less than +/−25 μm (0.001 in).

The backing plate 34 is attached to thermal control plate 16 by suitablefastener members described for example, in commonly-owned U.S. PatentApplication Publication No. 2007/0068629 which is incorporated herein byreference in its entirety. The backing member 34 contains a plurality ofholes 40 adapted to receive fastener members 42 for attaching thebacking member 34 to a thermal control plate 16.

EXAMPLES

Nonlimiting examples of sheet adhesive were formulated as describedabove, heat cured and tested. Test specimens were made of the sheetadhesive to simulate the performance of the sheet adhesive in a bondbetween mating surfaces, however it should be noted that test results ofactual bonds between electrodes and backing members are not shown here.Shear tests were conducted at room temperature and elevatedtemperatures, for example, at 180° C. Elevated temperature fatigue testswere conducted at, for example, 180° C. FIG. 14 shows a shear testresult of Example 1 sheet adhesive at room temperature. Example 1 showsa near linear stress-strain curve to over 300% shear strain and a lowshear stress at high shear strains. A bond made of such a soft sheetadhesive can be suitable to accommodate high shear strains withoutdiaphraming of bonded electrode and backing plates by coupling forces.

FIGS. 15 and 17 show a shear test result of Example 2 sheet adhesive at180° C. Example 2 experiences a near linear stress-strain curve to over300% shear strain at 180° C. and a low strength at high strains. Such asoft sheet adhesive bond can be suitable to accommodate high shearstrains without diaphraming of bonded electrode and backing plate.

FIG. 16 shows a fatigue test result of Example 3 sheet adhesive at 180°C. The fatigue test was conducted to more than 36,000 cycles (about35,000 shown). Although only specimens of sheet adhesive were tested,each cycle simulates a thermal cycle where a backing plate expands by adifferent amount than an electrode during plasma processing due todifferences in coefficients of thermal expansion of the materials of thebacking plate and electrode. FIG. 17 shows a shear test result ofExample 3 sheet adhesive at 180° C. after the fatigue test to over36,000 cycles. Example 3 exhibits a near linear stress-strain curve toover 300% shear strain at 180° C. and a low strength at high strains.For instance, Example 3 exhibits a near linear stress-strain curve in arange of about 0% to about 450% shear strain. Such a soft sheet adhesivebond can be suitable to accommodate high shear strains withoutdiaphraming of bonded electrode and backing plate even after over 36,000temperature cycles.

While the invention has been described in detail with reference tospecific embodiments thereof, it will be apparent to those skilled inthe art that various changes and modifications can be made, andequivalents employed, without departing from the scope of the appendedclaims.

What is claimed is:
 1. A method of joining components for a compositeshowerhead electrode assembly for a plasma processing apparatus,comprising: applying a first surface of a sheet of uncured elastomericadhesive in a predetermined pattern to a bottom surface of a backingmember in a predetermined pattern of bonding regions which excluderegions to remain unbonded, the backing member having a top surface anda plurality of first gas passages extending between the top surface andthe bottom surface and having outlets in unbonded regions; applying aprimer to the bottom surface of the backing member in a predeterminedpattern; applying a top surface of an electrode to a second surface ofthe sheet of uncured elastomeric adhesive in a predetermined pattern ofbonding regions, the electrode having a plasma exposed bottom surfaceand a plurality of second gas passages extending between the top surfaceand bottom surface of the electrode wherein the second gas passages haveinlets in unbonded regions of the top surface of the electrode; applyinga primer to the top surface of the electrode in a predetermined pattern;and bonding the top surface of the electrode to the bottom surface ofthe backing member with the sheet of elastomeric adhesive therebetweenwherein the second gas passages are in fluid communication with thefirst gas passages.
 2. The method of joining components for a compositeshowerhead electrode assembly of claim 1, wherein applying primer to thetop surface of the electrode comprises: rotating the electrode about itscenter point and depositing annular zones of the primer with a dispenserby contacting outlets of the dispenser with the rotating electrode atmultiple radial positions relative to the center point; or covering thetop surface with a mask having openings in a predetermined pattern andcoating the primer on unmasked regions of the top surface.
 3. The methodof joining components for a composite showerhead electrode assembly ofclaim 2, wherein the predetermined pattern in the mask is a plurality ofsemi-annular zones.
 4. The method of joining components for a compositeshowerhead electrode assembly of claim 1, wherein applying primer to thebottom surface of the backing member comprises: rotating the backingmember about its center point and depositing annular zones of the primerwith a dispenser by contacting outlets of the dispenser with therotating backing member at multiple radial positions relative to thecenter point; or covering the bottom surface with a mask having openingsin a predetermined pattern and coating the primer on unmasked regions ofthe bottom surface.
 5. The method of joining components for a compositeshowerhead electrode assembly of claim 1, wherein (a) applying the firstsurface of the sheet of elastomeric adhesive comprises precutting thesheet of elastomeric adhesive bonding material to the predeterminedpattern using one of mechanical cutting, die-cutting, laser cutting,water jet cutting, plasma cutting, plotter cutting and combinationsthereof; (b) the top surface of the electrode and/or the bottom surfaceof the backing member comprise channels over at least a portion of thepredetermined pattern; or (c) the sheet of elastomeric adhesive is afilled, uncured elastomeric silicone sheet wherein the filled, uncuredelastomeric silicone sheet is filled with thermally conductive particlesof aluminum, aluminum oxide, silicon, silicon carbide, boron nitride, oralloys thereof.
 6. The method of joining components for a compositeshowerhead electrode assembly of claim 1, wherein (a) bonding furthercomprises seating the sheet of elastomeric adhesive by pressing the topsurface of the electrode and the bottom surface of the backing membertogether under compression, under a static weight or optionally byatmospheric pressure within a vacuum bag, wherein the sheet ofelastomeric adhesive is heat curable; (b) heating the compositeshowerhead electrode assembly to cure the sheet of elastomeric adhesiveafter seating when the static weight or optional atmospheric pressurewithin a vacuum bag is removed; (c) the electrode is of silicon,graphite, or silicon carbide; and the backing member is of aluminum,graphite, or silicon carbide; (d) applying the first surface of thesheet of elastomeric adhesive comprises removing a transfer sheet fromthe first surface before applying the first surface to the bottomsurface of the backing member; (e) applying the top surface of theelectrode comprises removing a transfer sheet from the second surface ofthe sheet of elastomeric adhesive before applying the top surface of theelectrode to the second surface of the sheet of elastomeric adhesive;(f) applying the first surface of the sheet of elastomeric adhesivecomprises applying a vacuum after applying the first surface to thebottom surface of the backing member to remove gaps therebetween; (g)applying the top surface of the electrode comprises applying a vacuumafter applying the top surface of the electrode to the second surface ofthe sheet of elastomeric adhesive to remove gaps therebetween; or (h)the electrode comprises an inner showerhead electrode and an outer ringelectrode and the backing member comprises an inner backing plate and anouter backing ring.
 7. A method of processing a semiconductor substratein a plasma processing apparatus, the method comprising: placing asubstrate on a substrate support in a reaction chamber of a plasmaprocessing apparatus; introducing a process gas into the reactionchamber with a composite showerhead electrode assembly comprising: abacking plate comprising top and bottom surfaces with first gas passagestherebetween, the bottom surface having bonded and unbonded regions, thefirst gas passages having outlets in unbonded regions to supply aprocess gas to an interior of the plasma processing apparatus; anelectrode plate having a top surface, a plasma exposed bottom surface,and second gas passages extending therebetween and in fluidcommunication with the first gas passages, wherein the second gaspassages have inlets in unbonded regions of the top surface of theelectrode plate; and an elastomeric sheet adhesive joint disposedbetween mating surfaces at each of the bonded regions which allowsmovement in a lateral direction of the electrode plate relative to thebacking plate during temperature cycling due to mismatch of coefficientsof thermal expansion in the electrode plate and the backing plate;generating a plasma from the process gas in the reaction chamber betweenthe composite showerhead electrode assembly and the substrate;processing the substrate with the plasma; wherein the elastomeric sheetadhesive joint further comprises a primer on one or more of the matingsurfaces of the backing member and/or the electrode.
 8. The method ofclaim 7, wherein the elastomeric sheet adhesive joint comprises athermally conductive silicone adhesive sheet.
 9. The method of claim 8,wherein the thermally conductive silicone adhesive sheet comprises twoor more laminated layers having different physical properties and/or thethermally conductive silicone adhesive sheet comprises two or moreco-planar portions having different physical properties.
 10. The methodof claim 8, wherein at least one portion of the thermally conductivesilicone adhesive sheet has a thermal conductivity of 0.5 W/mK to 0.8W/mK, at least one portion of the thermally conductive silicone adhesivesheet has a thermal conductivity of 0.8 W/mK to 1 W/mK and/or at leastone portion of the conductive silicone adhesive sheet has a thermalconductivity of over 1 W/mK.
 11. The method of claim 8, wherein thethermally conductive silicone adhesive sheet comprises a uniformdistribution of thermally conductive filler.
 12. The method of claim 11,wherein (a) the thermally conductive filler is one of boron nitride(BN), aluminum oxide (Al₂O₃), silicon, silicon carbide, and acombination thereof or (b) the thermally conductive silicone adhesivesheet is of (i) high molecular weight dimethyl silicone and thethermally conductive filler, (ii) high molecular weight dimethylsilicone and the thermally conductive filler matrixed around fiberglassscreen (scrim), (iii) high molecular weight dimethyl silicone and thethermally conductive filler matrixed around metallic screen or (iv) highmolecular weight dimethyl silicone and the thermally conductive fillermixed with glass microbeads, or nanobeads.
 13. The method of claim 7,wherein the processing comprises etching the substrate.
 14. The methodof claim 7, wherein the backing plate comprises an inner backing plateand an outer backing ring, the outer backing ring surrounding the innerbacking plate, wherein the first gas passages are in the inner backingplate, and the electrode plate comprises an inner showerhead electrodebonded to the inner backing plate and an outer ring electrode bonded tothe outer backing ring, wherein the second gas passages are in the innershowerhead electrode.
 15. The method of claim 7, wherein (a) the matingsurface of the backing plate is parallel to the mating surface of theshowerhead electrode and/or (b) the electrode is of single crystalsilicon, polycrystalline silicon, graphite or silicon carbide; and thebacking member is of aluminum, graphite, or silicon carbide.
 16. Themethod of claim 7, wherein the elastomeric sheet adhesive joint iselastically deformable in the lateral direction to at least 200% shearstrain from a shear stress of about 20 to 340 psi in a temperature rangeof room temperature to 300° C.
 17. The method of claim 16, wherein theelastomeric sheet adhesive joint is elastically deformable in thelateral direction to at least 300% shear strain from a shear stress ofabout 20 to 80 psi.
 18. The method of claim 7, wherein the electrodeplate is a disk of single crystal silicon with a diameter of at least200 mm and the elastomeric sheet adhesive joint is elasticallydeformable in the lateral direction to at least 200% shear strain from ashear stress of about 20 to 340 psi in a temperature range of roomtemperature to 300° C. after 5000 temperature cycles of heating theshowerhead electrode assembly from room temperature to 250° C.
 19. Themethod of claim 7, wherein a gap distance between the mating surfacesvaries by less than ±25 μm (0.001 in).
 20. The method of claim 7,wherein (a) the elastomeric sheet adhesive joint comprises anelastomeric sheet adhesive cast or rolled into a pre-form shape; (b) theelastomeric sheet adhesive joint comprises an elastomeric sheet adhesiveof die cut pre-form shape; (c) the elastomeric sheet adhesive jointcomprises an elastomeric sheet adhesive laser cut, plotter cut and/orwater jet cut pre-form shape; or (d) one of the mating surfacescomprises a cavity.
 21. The method of claim 20, wherein (a) the cavitydepth is in a range of 100 to 200 μm; (b) the cavity depth is in a rangeof 200 to 500 μm; (c) the cavity comprises an elevation jog sized tomatch a dimension of the sheet adhesive; (d) the elastomeric sheetadhesive bonds the top surface of the electrode to the bottom surface ofthe backing member with a spacing therebetween of 50 to 400 μm; (e) theelastomeric sheet adhesive comprises a silicone adhesive sheet in a formof a single sheet; (f) the elastomeric sheet adhesive comprises asilicone adhesive sheet in a form of one or more flat rings, flat ringswith elevation jogs, cylinders, flat or columnar polygons, blocks orcombination thereof; or (g) the elastomeric sheet adhesive comprises aheat cured adhesive.